docs: def pypy_version_monkeypatch():
      """Patch Tox to work with non-default PyPy 3 versions."""
      # Travis virtualenv do not provide `pypy3`, which tox tries to execute.
      # This doesnt affect Travis python version `pypy3`, as the pyenv pypy3
      # is in the PATH.
      # https://github.com/travis-ci/travis-ci/issues/6304
      # Force use of the virtualenv `python`.
      version = os.environ.get('TRAVIS_PYTHON_VERSION')
      if version and default_factors and version.startswith('pypy3.3-'):
          default_factors['pypy3'] = 'python'